1. Field of the Invention
The present invention relates to a method of producing a glycolic acid ester.
More particularly, the present invention relates to a method of producing a glycolic acid ester by a catalytic hydrogenation of an oxalic acid diester with a high selectivity and with a high yield.
The glycolic acid esters are significantly useful as a material for cleaning agent for a boiler and the like, an additive for plating, an etching agent and an tanning agent for leather and an intermediate for preparing detergent builders and for biodegradable polymers.
2. Description of the Related Art
As a method for producing a glycolic acid ester, a catalytic reaction method of an oxalic acid diester, for example, diethyl oxalate with hydrogen in the presence of a catalyst is known from, for example, Japanese Examined Patent Publication (Kokoku) No. 55-42971, U.S. Pat. No. 4,112,245, and German Patent No. 459,603. The method as disclosed in those publications is disadvantageous in that since the reaction is a successive reaction, if the catalyst used and the reaction conditions applied are not optimum, the reaction proceeds excessively so that an undesirable ethylene glycol is produced as a by-product and thus the selectivity of the desired glycolic acid ester is reduced. Also, the by-product causes the isolation and collection of the desired glycolic acid ester to be complicated.
To solve the above-mentioned problem, for example, in GB-B-2,031,883, it was attempted to catalytically react an oxalic acid diester with hydrogen in the presence of a catalyst comprising at least one member selected from ruthenium, nickel and Raney nickel under specific reaction conditions. By this method, a reaction product comprising one of ethylene glycol and glycolic acid ester in a relatively large amount is obtained.
However, to industrially produce glycolic acid ester, the above-mentioned method must be improved so that the reaction rate is enhanced and the selectivity of glycolic acid ester is increased. Also, it is necessary that a cheap catalyst is allowed to be used and the reaction conditions are made mild.
U.S. Pat. No. 4,585,890 discloses a catalyst, in which an amine complex of copper is carried on a silica carrier, for the catalytic reaction. Also, U.S. Pat. No. 4,409,395 discloses a catalyst in which silver or palladium is carried on a carrier, for the catalytic reaction. However, those catalysts are unsatisfactory in that the catalytic activity of the catalysts and the resultant selectivity of glycolic acid ester are low and thus they are not appropriate for practical use.
As mentioned above, the conventional methods for producing the glycolic acid ester are disadvantageous in that since the hydrogenation of an oxalic acid diester is effected by a successive reaction, the progress of the reaction causes an undesirable production of ethylene glycol as a by-product, and thus the resultant glycolic acid ester is obtained with a poor selectivity thereof.
Accordingly, a new method of producing a glycolic acid ester by a Catalytic reaction with an enhanced selectivity of the glycolic acid ester and with a high yield, is needed.